Support atomic vector ptype in list_flatten()

Allows implementing e.g. `rlang::flatten_int()`

R/flatten.R

@@ -36,10 +36,16 @@ list_flatten <- function(x, ..., ptype = x, name_spec = NULL) {
   ellipsis::check_dots_empty()
   list_assert(x)
 
-  # Wrap any non-list elements
-  out <- map_if(x, negate(vec_is_list), list)
+  if (vec_is_list(ptype)) {
+    # Wrap any non-list elements so all the elements to concatenate are lists
+    out <- map_if(x, negate(vec_is_list), list)
+  } else {
+    # Unchop all list elements so all the elements to concatenate are of type `ptype`
+    out <- map_if(x, vec_is_list, vec_unchop, ptype = ptype, name_spec = name_spec)
+  }
 
-  # Concatenate the elements (now all lists) in a single list
+  # Concatenate the elements (now all lists or all vectors) in a
+  # vector of type `ptype`
   vec_unchop(out, ptype = ptype, name_spec = name_spec)
 }
 

tests/testthat/test-flatten.R

@@ -35,3 +35,18 @@ test_that("list_flatten() creates output of type `ptype`", {
     new_count_list(list(1, 2))
   )
 })
+
+test_that("list_flatten() creates atomic vectors if requested", {
+  expect_identical(
+    list_flatten(list(1, list(2)), ptype = int()),
+    1:2
+  )
+  expect_identical(
+    list_flatten(
+      list(x = 1, y = list(foo = 2)),
+      ptype = int(),
+      name_spec = "{outer}_{inner}"
+    ),
+    c(x = 1L, y_foo = 2L)
+  )
+})